Method of manufacturing capacitor of semiconductor device

ABSTRACT

A method of manufacturing a capacitor of a semiconductor device, according to the present invention comprises the steps of heat-treating a Ta 2 O 5  film formed on a metal or metal oxide electrode corresponding to a lower electrode of the capacitor at a temperature lower than a temperature at which the Ta 2 O 5  film is crystallized, and thereafter heat-treating the Ta 2 O 5  film at a temperature higher than or equal to the crystallizing temperature of the Ta 2 O 5  film.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method of manufacturing a capacitor of asemiconductor device. The present invention relates particularly to amethod of annealing a Ta₂O₅ film having a high relative dielectricconstant, which is formed on a metal or metal oxide electrode.

2. Description of the Related Art

A relative dielectric constant of a Ta₂O₅ film formed on polycrystalsilicon ranges from 20 to 28. This relative dielectric constant is threetimes or more than that of a silicon nitride film. Therefore, theintroduction of the Ta₂O₅ film into a process has been studied with theTa₂O₅ film as a DRAM (Dynamic Random Access Memory) capacitor dielectricof 256 Mbit or later.

It has recently been reported and noted that a Ta₂O₅ film formed on anelectrode composed of a metal such as Pt, Ru or the like has indicated arelative dielectric constant close to 50.

A Ta₂O₅ film immediately after its deposition, which has been formed byCVD (Chemical Vapor Deposition), produces a large leakage current. Aproblem on such a leakage current characteristic can be improved by postanneal subsequent to the above formation.

This point of view will be described in detail. Many impurities causedby a raw gas are contained in the Ta₂O₅ film obtained immediately afterits formation. Oxygen is also often deficient in the Ta₂O₅ film. Theseimpurities and oxygen deficiencies are considered to serve as currentpaths and thereby result in a large leakage current flow.

Therefore, the Ta₂O₅ film is heat-treated at a high temperature near800° C. in an atmosphere of oxygen or at a comparatively low temperatureof 400° C. or less in an atmosphere of ozone or nitrogen oxide to reducethe impurities and oxygen deficiencies in the Ta₂O₅ film, whereby theleakage current can be greatly reduced.

However, if the Ta₂O₅ film deposited on the metal electrode ispost-annealed at a temperature of 600° C. or less, it is then kept in anamorphous state. Thus, the relative dielectric constant thereof resultsin about 25 similar to the value of a Ta₂O₅ film on a silicon electrodeand the leakage current is less than or equal to 10⁻⁸ (A/cm⁻²).

On the other hand, when the Ta₂O₅ film on the metal electrode isheat-treated at a high temperature of 700° C. or more, the Ta₂O₅ film iscrystallized so that its relative dielectric constant is increased toabout 50. However, the leakage current is increased by one digit or moreas compared with the Ta₂O₅ film kept in the amorphous state.

Therefore, the implementation of the Ta₂O₅ film on the metal electrode,which is indicative of the large relative dielectric constant of 50 ormore, needs to decrease the leakage current in the crystallized Ta₂O₅film.

SUMMARY OF THE INVENTION

With the foregoing in view, it is therefore an object of the presentinvention to provide a method of manufacturing a capacitor of asemiconductor device, which improves a method of annealing a Ta₂O₅ filmformed on a metal or metal oxide electrode, thereby making it possibleto crystallize a Ta₂O₅ film and limit a leakage current flow as low aspossible.

According to one aspect of the present invention, for achieving theabove object, there is provided a method of manufacturing a capacitor ofa semiconductor device, comprising the following steps of:

a step for forming a metal or metal oxide electrode over a semiconductorsubstrate;

a step for forming a Ta₂O₅ film on the metal or metal oxide electrode;

a step for heat-treating the Ta₂O₅ film at a temperature lower than acrystallizing temperature of the Ta₂O₅ film to compensate for oxygendeficiencies and remove impurities; and

a step for heat-treating the Ta₂O₅ film at a temperature higher than orequal to the crystallizing temperature of the Ta₂O₅ film after saidheat-treating step to crystallize the Ta₂O₅ film.

Typical ones of various inventions of the present application have beenshown in brief. However, the various inventions of the presentapplication and specific configurations of these inventions will beunderstood from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing outand distinctly claiming the subject matter which is regarded as theinvention, it is believed that the invention, the objects and featuresof the invention and further objects, features and advantages thereofwill be better understood from the following description taken inconnection with the accompanying drawings in which:

FIG. 1 is a cross-sectional view for describing a method ofmanufacturing a capacitor of a semiconductor device, which shows a firstembodiment of the present invention;

FIG. 2 is a cross-sectional view for describing a method ofmanufacturing a capacitor of a semiconductor device, which shows asecond embodiment of the present invention;

FIG. 3 is a cross-sectional view for describing a method ofmanufacturing a capacitor of a semiconductor device, which shows a thirdembodiment of the present invention; and

FIG. 4 is a cross-sectional view for describing a method ofmanufacturing a capacitor of a semiconductor device, which shows afourth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will hereinafter bedescribed in detail with reference to the accompanying drawings.

FIG. 1 is a cross-sectional view for explaining a method ofmanufacturing a capacitor of a semiconductor device, which illustrates afirst embodiment of the present invention.

As shown in FIG. 1(a), a contact hole is first defined in an interlayerinsulator (SiO₂ film) 12 formed on a substrate 11. Polycrystal silicon13 for contact is then embedded into the contact hole. A lower electrode14 composed of a metal or metal oxide (such as Pt, Ru or RuO2, IrO2) isformed on the polycrystal silicon 13 and the interlayer insulator 12.

Next, a Ta₂O₅ film 15 is formed as shown in FIG. 1(b). Thereafter, theTa₂O₅ film 15 is heat-treated at a temperature of about 600° C. lowerthan a crystallizing temperature of the Ta₂O₅ film for about an hour inan atmosphere of oxygen.

The Ta₂O₅ film 15 is then subjected to RTA (Rapid Thermal Annealing) ata temperature higher than or equal to the crystallizing temperature ofthe Ta₂O₅ film as shown in FIG. 1(c), so that a crystallized and highrelative dielectric Ta₂O₅ film 15′ is formed. In the present embodiment,the reaction other than the crystallization of the Ta₂O₅ film can berestrained by rapidly increasing the temperature for the Ta₂O₅ film toan intended temperature at 100° C./sec or above, using a lamp annealer,for example.

Finally, an upper electrode 16 is deposited on the crystallized Ta₂O₅film 15′ to form a capacitor cell as shown in FIG. 1(d).

In the first embodiment, the initial heat treatment of the Ta₂O₅ film isdone at the temperature (of about 600° C.) lower than the crystallizingtemperature of Ta₂O₅ film for about one hour in the atmosphere ofoxygen. It is thus possible to sufficiently compensate for a oxygendeficiencies in the Ta₂O₅ film and remove impurities in the Ta₂O₅ film.Thereafter, the resultant product is subjected to RTA at a hightemperature above 700° C. for about one minute so as to crystallize theTa₂O₅ film. As a result, a large relative dielectric constant of theTa₂O₅ film is obtained.

Thus, the Ta₂O₅ film having the high relative dielectric constant, whichis able to restrict a leakage current flow, is formed on the metal ormetal oxide electrode by crystallizing the Ta₂O₅ film after the cause ofthe leakage current has sufficiently been decreased by the initiallow-temperature anneal.

FIG. 2 is a cross-sectional view for describing a method ofmanufacturing a capacitor of a semiconductor device, which illustrates asecond embodiment of the present invention.

An interlayer insulator (SiO₂ film) 22 is first formed on asemiconductor substrate 21 as shown in FIG. 2(a). A contact hole is thendefined in the interlayer insulator 22. Polycrystal silicon 23 forcontact is embedded into the contact hole. A lower electrode 24 composedof a metal or metal oxide (such as Pt, Ru or RuO2, IrO2) is formed onthe polycrystal silicon 23 and the interlayer insulator 22.

Next, a Ta₂O₅ film 25 is formed on the metal or metal oxide electrode asshown in FIG. 2(b). Thereafter, the Ta₂O₅ film 25 is heat-treated at atemperature of about 600° C. lower than a crystallizing temperature ofthe Ta₂O₅ film for about one hour in an atmosphere of oxygen.

Next, the Ta₂O₅ film is subjected to heat treatment at a hightemperature (700° C. or above) for crystallizing the Ta₂O₅ film, using adiffusion furnace as shown in FIG. 2(c). Described specifically, thetemperature to be applied to the Ta₂O₅ film is increased to a targettemperature at about 100° C./sec and the Ta₂O₅ film is subjected to heattreatment for about one hour. Thereafter, the so heat-treated Ta₂O₅ filmis reduced in temperature at about 10° C./sec. As a result, acrystallized and high relative dielectric Ta₂O₅ film 25′ is formed.

Finally, an upper electrode 26 is deposited on the crystallized Ta₂O₅film 25′ to form a capacitor cell as shown in FIG. 2(d).

In the second embodiment, the initial heat treatment of the Ta₂O₅ filmis carried out at the temperature (about 600° C.) lower than thecrystallizing temperature of Ta₂O₅ film for about one hour in theatmosphere of oxygen. It is thus possible to sufficiently compensate foroxygen deficiencies in the Ta₂O₅ film and remove impurities in the Ta₂O₅film. Thereafter, a large crystal is grown by high-temperature heattreatment in the diffusion furnace, so that the Ta₂O₅ film with lesscrystal grain boundary is obtained in the Ta₂O₅ film.

Thus, the initial low-temperature anneal compensates for oxygendeficiencies in the Ta₂O₅ film and allows the removal of the impuritiesin the Ta₂O₅ film. A Ta₂O₅ film having a high relative dielectricconstant, which further restricts a leakage current, can be formed onthe metal or metal oxide electrode by reducing the crystal grainboundary at the crystallization of the Ta₂O₅ film with the subsequentanneal.

A third embodiment will next be described.

FIG. 3 is a cross-sectional view for describing a method ofmanufacturing a capacitor of a semiconductor device, which shows thethird embodiment of the present invention.

The present embodiment is a two-step anneal method using a gas strongerthan oxygen in oxidizing force.

An interlayer insulator (SiO₂ film) 32 is first formed on asemiconductor substrate 31 as shown in FIG. 3(a). A contact hole isdefined in the interlayer insulator 32. Polycrystal silicon 33 forcontact is embedded into the contact hole. A lower electrode 34 composedof a metal or metal oxide (such as Pt, Ru or RuO2, IrO2) is formed onthe polycrystal silicon 33 and the interlayer insutator 32.

Next, a Ta₂O₅ film 35 is formed on the metal or metal oxide electrode asshown in FIG. 3(b). Thereafter, the Ta₂O₅ film 35 is heat-treated at atemperature of about 300° C. using O₃ or at a temperature of about 600°C. lower than a crystallizing temperature of the Ta₂O₅ film for aboutone hour in the atmosphere using N₂O or the like, which is strong inoxidizing force.

Next, the Ta₂O₅ film 35 is heat-treated at a high temperature (700° C.or more) for crystallizing the Ta₂O₅ film as shown in FIG. 3(c). As aresult, a crystallized and high relative dielectric Ta₂O₅ film 35′ isformed.

Finally, an upper electrode 36 is deposited on the Ta₂O₅ film 35′ toform a capacitor cell as shown in FIG. 3(d).

Since the initial heat treatment of the Ta₂O₅ film is conducted in theatmosphere of O₃ strong in oxidizing force or the atmosphere of N₂O orthe like in the third embodiment, the compensation for the oxygendeficiencies in the Ta₂O₅ film is effectively carried out as comparedwith the first embodiment. Thereafter, the high-temperature heattreatment for crystallizing the Ta₂O₅ film is carried out. As a result,a Ta₂O₅ film having a high dielectric constant, which further limits aleakage current, can be formed on the metal or metal oxide electrode.

A fourth embodiment will next be described.

FIG. 4 is a cross-sectional view for describing a method ofmanufacturing a capacitor of a semiconductor device, which shows thefourth embodiment of the present invention.

The present embodiment is a two-step anneal method using an atmosphereunder which the oxidizing force of oxygen is enhanced by light or plasmaexcitation.

An interlayer insulator (SiO₂ film) 42 is first formed on asemiconductor substrate 41 as shown in FIG. 4(a). A contact hole isdefined in the interlayer insulator 42. Polycrystal silicon 43 forcontact is embedded into the contact hole. A lower electrode 44 composedof a metal or metal oxide (Pt, RU or RuO2, IrO2) is formed on thepolycrystal silicon 43 and the interlayer insutator 42.

Next, a Ta₂O₅ film 45 is formed on the lower electrode 44 as shown inFIG. 4(b). Thereafter, the Ta₂O₅ film 45 is subjected to UV light 47having a wavelength of about 200 nm for about one hour at a temperaturebelow 670° C. lower than a temperature at which the Ta₂O₅ film iscrystallized. Further, the so-processed Ta₂O₅ film 45 is heat-treated inan activated atmosphere of oxygen.

Next, the Ta₂O₅ film 45 is heat-treated at a high temperature (700° C.or more) for crystallizing the Ta₂O₅ film. As a result, a crystallizedand high relative dielectric Ta₂O₅ film 45′ is formed.

Finally, an upper electrode 46 is deposited on the crystallized Ta₂O₅film 45′ to form a capacitor cell as shown in FIG. 4(d).

In the fourth embodiment, since the initial heat treatment of the Ta₂O₅film is performed in the oxygen atmosphere activated by the UV light orthe like, the compensation for the oxygen deficiencies in the Ta₂O₅ filmand the removal of impurities in the Ta₂O₅ film are effectively done ascompared with the first embodiment. Thereafter, since thehigh-temperature heat treatment for crystallizing the Ta₂O₅ film iscarried out, a Ta₂O₅ film having a high dielectric constant, which iscapable of further limiting the flow of a leakage current, can be formedon the metal or metal oxide electrode.

According to the present invention, if a Ta₂O₅ film is of a lowerelectrode indicative of a larger relative dielectric constant due to itscrystallization, then the same anneal method as described above isapplicable to all metals or metal oxides as a method of reducing aleakage current developed in the Ta₂O₅ film.

While the present invention has been described with reference to theillustrative embodiments, this description is not intended to beconstrued in a limiting sense. Various modifications of the illustrativeembodiments, as well as other embodiments of the invention, will beapparent to those skilled in the art on reference to this description.It is therefore contemplated that the appended claims will cover anysuch modifications or embodiments as fall within the true scope of theinvention.

What is claimed is:
 1. A method of manufacturing a capacitor of asemiconductor device, comprising: forming a metal or metal oxideelectrode over a semiconductor substrate; forming a Ta₂O₅ film on themetal or metal oxide electrode; heat-treating the Ta₂O₅ film at atemperature lower than a crystallizing temperature of the Ta₂O₅ film tocompensate for oxygen deficiencies and remove impurities; andheat-treating the Ta₂O₅ film having been subjected to said heat-treatingat the temperature lower than the crystallizing temperature of the Ta₂O₅film at a temperature higher than or equal to the crystallizingtemperature of the Ta₂O₅ film after said heat-treating step tocrystallize the Ta₂O₅ film.
 2. A method according to claim 1, whereinsaid heat-treating the Ta₂O₅ film at the temperature lower than thecrystallizing temperature of the Ta₂O₅ film is carried out in anoxidative atmosphere.
 3. A method according to claim 2, wherein saidheat-treating the Ta₂O₅ film at the temperature higher than or equal tothe crystallizing temperature of the Ta₂O₅ film is a rapid heat-treatingstep.
 4. A method according to claim 1, wherein said heat-treating theTa₂O₅ film at the temperature higher than or equal to the crystallizingtemperature of the Ta₂O₅ film is carried out through a diffusion furnaceso as to obtain the Ta₂O₅ film having less crystal grain boundary.
 5. Amethod according to claim 1, wherein said heat-treating the Ta₂O₅ filmat the temperature lower than the crystallizing temperature of the Ta₂O₅film is carried out in an atmosphere of O₃ or N₂O.
 6. A method accordingto claim 1, wherein said heat-treating the Ta₂O₅ film at the temperaturelower than the crystallizing temperature of the Ta₂O₅ film is carriedout in an oxidative atmosphere activated by light or plasma excitation.7. A method according to claim 1, wherein said heat treating at thetemperature lower than the crystallizing temperature does not includerapid thermal annealing.
 8. A method according to claim 1, wherein saidheat treating at the temperature lower than the crystallizingtemperature produces substantially no crystallization of the Ta₂O₅.
 9. Amethod of manufacturing a capacitor of a semiconductor device,comprising: forming a metal or metal oxide electrode over asemiconductor substrate; forming a Ta₂O₅ film on the metal or metaloxide electrode; heat-treating the Ta₂O₅ film at a temperature lowerthan a crystallizing temperature of the Ta₂O₅ film; and heat-treatingthe Ta₂O₅ film having been subjected to said heat-treating at thetemperature lower than the crystallizing temperature of the Ta₂O₅ filmat a temperature higher than or equal to the crystallizing temperatureof the Ta₂O₅ film after said heat-treating step to crystallize the Ta₂O₅film.
 10. A method according to claim 9, wherein said heat-treating theTa₂O₅ film at the temperature lower than the crystallizing temperatureof the Ta₂O₅ film is carried out in an oxidative atmosphere.
 11. Amethod according to claim 9, wherein said heat-treating the Ta₂O₅ filmat the temperature higher than or equal to the crystallizing temperatureof the Ta₂O₅ film is a rapid heat-treating step.
 12. A method accordingto claim 9, wherein said heat-treating the Ta₂O₅ film at the temperaturehigher than or equal to the crystallizing temperature of the Ta₂O₅ filmis carried out through a diffusion furnace so as to obtain the Ta₂O₅film having less crystal grain boundary.
 13. A method according to claim9, wherein said heat-treating the Ta₂O₅ film at the temperature lowerthan the crystallizing temperature of the Ta₂O₅ film is carried out inan atmosphere of O₃ or N₂O.
 14. A method according to claim 9, whereinsaid heat-treating the Ta₂O₅ film at the temperature lower than thecrystallizing temperature of the Ta₂O₅ film is carried out in anoxidative atmosphere activated by light or plasma excitation.
 15. Amethod according to claim 9, wherein said heat treating at thetemperature lower than the crystallizing temperature does not includerapid thermal annealing.
 16. A method according to claim 9, wherein saidheat treating at the temperature lower than the crystallizingtemperature produces substantially no crystallization of the Ta₂O₅ film.